Imaging devices in which a plurality of charge coupled devices (CCDs), complementary metal-oxide semiconductor (CMOS) elements, and the like are two-dimensionally arranged are used these days in digital video cameras, digital still cameras, and the like. An imaging device is manufactured by forming photoelectric conversion portions and a diffusion layer through impurity introduction such as ion implantation into a substrate, and then depositing and processing films to form wiring layers and insulating films. Light that has entered the imaging device is absorbed by the photoelectric conversion portions, and is converted into electric charge. This electric charge is accumulated in the photoelectric conversion portions, and the total amount of the accumulated electric charge is detected. Thus, a signal corresponding to the incident light intensity is acquired.
However, if the penetration length of incident light is greater than the depth of the substrate, the incident light is not sufficiently absorbed by the photoelectric conversion portions, and part of the incident light passes through the substrate. As a result, the part of the incident light is not converted into a charge signal, and light use efficiency becomes lower. Patent Document 1 suggests improving sensitivity by effectively performing photoelectric conversion on light that has passed through the photoelectric conversion portions and has a long wavelength.